The present invention relates to an electronic device, a method of manufacturing the same, and an apparatus for manufacturing the same. The present invention relates to an electronic device of a semiconductor device such as, for example, a leadless small surface mount transistor or diode, a method of manufacturing the same, and an apparatus for manufacturing the same.
FIGS. 9A to 9C show a structural example of a conventional leadless small surface mount transistor: FIG. 9A is its plan view; FIG. 9B is its sectional side view; and FIG. 9C is its bottom view.
As shown in FIGS. 9A and 9B, a leadless small surface mount electronic device 3 includes: a first upper electrode 11 provided with an element mount portion on an upper surface 321 of a ceramic substrate 32; and a second upper electrode 12 and a third upper electrode 13 that are positioned so as to be separated from the first upper electrode 11.
On the back surface of a semiconductor chip on which a transistor 14 is formed, for instance, a collector electrode is formed by metal deposition or the like. The collector electrode of the transistor 14 is fixed to the first upper electrode 11 by die bonding or the like and thus the first upper electrode 11 is electrically connected to the collector electrode of the transistor 14.
The second upper electrode 12 and for example, a base electrode of the transistor 14 are connected with a metal wire 15. Similarly, the third upper electrode 13 and for example, an emitter electrode of the transistor 14 are connected with a metal wire 16. A pair of lower electrodes 21 and 22 electrically connected to the first upper electrode 11 are formed on a lower surface 322 of the ceramic substrate 32. The first upper electrode 11 and the pair of lower electrodes 21 and 22 are electrically connected through conductive relay members going through the ceramic substrate 32, i.e. via holes 17 and 18.
Similarly, on the lower surface 322 of the ceramic substrate 32, lower electrodes 23 and 24 are formed, which are electrically connected to the second upper electrode 12 and the third upper electrode 13 through via holes 19 and 20 going through the ceramic substrate 32, respectively.
As shown in FIG. 9C, the lower electrodes 21, 22, 23, and 24 are positioned at the four corners of the lower surface 322 of the ceramic substrate 32.
These lower electrodes 21 to 24 are attached, for example, to a wiring pattern provided in a printed circuit board, which is not shown in the figure, with a conductive adhesive such as solder or the like.
FIGS. 10A and 10B show a so-called master electronic device in which a plurality of individual electronic devices are formed, which is divided into individual electronic devices as shown in FIGS. 9A to 9C later. In other words, as shown in FIG. 10A, mxc3x97n pieces of electronic devices 3 are formed on one common ceramic substrate 32 in a matrix form. In the respective electronic devices 3, electronic elements such as a transistor, a diode, a resistor, and the like already have been mounted on a wiring pattern (electrode) formed on the ceramic substrate 32. In addition, predetermined electrodes of the electronic elements, for example, a collector electrode, a base electrode, and an emitter electrode of the transistor are connected to the wiring pattern (electrode) provided on the ceramic substrate directly or via metal wires or the like.
After that, as shown in FIG. 10B, generally the upper surface of the electrode ceramic substrate 32 is coated with liquid resin 26 by a potting method, a dispenser method, a vacuum printing method, or the like. The liquid resin 26 is cured by heating, and thus the upper surface is sealed with the resin. Then, the master electronic device is divided into individual electronic devices along cutting plane lines 33 (FIG. 10A) by a dicing saw.
Generally, the conventional leadless small surface mount electronic device is obtained by allowing liquid resin to form a resin package by the potting method, the dispenser method, the vacuum printing method, or the like and then curing the resin in a curing oven or the like. However, the material obtained by curing the liquid resin has a glass transition point of about 100xc2x0 C., which is low. Therefore, when solder reflow is carried out at 230xc2x0 C., the resin that has been cured is resoftened and therefore the resin thus softened is peeled off from the ceramic substrate easily, which has been a problem.
Furthermore, in the potting method and the dispenser method, the liquid resin merely is dropped or poured onto the ceramic substrate and then is cured without being molded under pressure, thus forming a resin package. Therefore, there have been the following problems. As shown in FIG. 9B, not only unevenness d1 in thickness of the resin that has been cured is caused but also it is difficult to increase the density of the resin. Thus, the strength of the resin is low, and when subjected to an external stress, the resin package is deformed easily.
Similarly, in the vacuum printing method, liquid resin simply is applied onto the ceramic substrate using a printing means and then is cured. Therefore, there has been a problem that an unevenness d1 in thickness of about 5 to 15 xcexcm occurs in the resin that has been cured.
As described above, in the conventional formation methods, not only has the difference in thickness of the resin in an electronic device been caused to increase an irregularity of its surface, but also between electronic devices the difference in thickness of the resin has been caused. Therefore, there has been a problem that after the formation by resin sealing, after-processing such as grinding of the resin surface using a grindstone or the like must be carried out.
As shown in FIG. 10B, when using the liquid resin, the thickness of the resin increases in the peripheral portion of the ceramic substrate and is uniform only in the vicinity of the center of the substrate. The difference d2 in thickness of the resin between the vicinity of the center and the peripheral portion of the ceramic substrate reaches about 0.1 mm.
Furthermore, there have been the following problems. In a dicing step for forming individual packages, it is difficult to allow the resin surface of the electronic device to adhere to a fixing tape or the like due to the irregularities d1 and d2 on the surface of the electronic device after the resin is cured. In addition, the individual electronic devices cut in dicing come off from the fixing tape and thus are lost easily.
In the resin sealing by a transfer molding method using a mold, which has been known conventionally as a method of sealing a semiconductor, the ceramic substrate is not easily bent compared to other resin substrates or metal lead frames. Therefore, due to the distortion caused by pressure applied when the ceramic substrate is sandwiched between upper and lower molds, cracks or breakage occur easily in the ceramic substrate. Consequently, the resin sealing by the transfer molding method was not employed for the conventional leadless small surface mount transistor.
In order to solve the aforementioned conventional problems, the present invention is intended to provide an electronic device, a method of manufacturing the same, and an apparatus for manufacturing the same, wherein the occurrence of cracks or breakage in a ceramic substrate can be prevented by buffering the pressure applied to the ceramic substrate so as to prevent a distortion force from being caused even when the ceramic substrate is sandwiched and compressed between upper and lower molds.
In order to achieve the above-mentioned object, an electronic device of the present invention is obtained by mounting plural sets of electronic components on a ceramic substrate and sealing the electronic components with thermosetting resin by transfer molding. The electronic device is provided with a metallic thin film integrated into at least one selected from an upper surface and a lower surface of the ceramic substrate at its peripheral portion.
As the metallic thin film, upper electrodes provided on the ceramic substrate also can be used. That is to say, the metallic thin film includes one utilizing electrodes.
A method of manufacturing an electronic device according to the present invention includes: mounting plural sets of electronic components on a ceramic substrate; and sealing the electronic components with thermosetting resin by transfer molding. In the method, the ceramic substrate provided with a metallic thin film integrated into at least one selected from an upper surface and a lower surface of the ceramic substrate in its peripheral portion is placed so as to extend both inside and outside a cavity of a mold for transfer molding and the metallic thin film is positioned in a portion with which an upper mold and a lower mold of the mold come into contact, and the thermosetting resin for transfer molding is injected into the cavity, is molded, and then is cured by heating.
An apparatus for manufacturing an electronic device according to the present invention includes: a plunger for pressurizing thermosetting resin for transfer molding; a runner in which the thermosetting resin for transfer molding flows; a cavity into which the thermosetting resin for transfer molding flows, which communicates with the runner; and a mold for transfer molding including an upper mold and a lower mold that define the cavity. In the apparatus, a ceramic substrate provided with a metallic thin film integrated into at least one selected from an upper surface and a lower surface of the ceramic substrate in its peripheral portion is placed so as to extend both inside and outside the cavity of the mold for transfer molding, and the metallic thin film is positioned in a portion with which the upper mold and the lower mold of the mold come into contact, and the thermosetting resin for transfer molding is injected into the cavity, is molded, and then is cured by heating.
According to the present invention, the ceramic substrate provided with the metallic thin film integrated into at least one selected from the upper surface and the lower surface of the ceramic substrate in its peripheral portion is placed so as to extend both inside and outside the cavity of the mold for transfer molding, and the metallic thin film is positioned in a portion with which the upper mold and the lower mold of the mold come into contact. Therefore, even when the ceramic substrate is sandwiched and compressed between the upper and lower molds, the pressure applied to the ceramic substrate is buffered. Thus, no distortion force is caused and the occurrence of cracks or breakage in the ceramic substrate can be prevented.